Volume 15, Number 4, December 1999
By Dieter Bilitza and Natalia Papitashvili
The Web interface to the International Reference Ionosphere (IRI) model (IRIWeb) continues to be one of NSSDC's very popular services with over 2,000 accesses per month. The IRIWeb lets users list and plot output parameters for specified input parameters. Inputs are the date, time, and location, while outputs are the ionospheric electron density; ion composition (O+, H+, He+, NO+, O2+, N2+, Cluster-ions); and the electron, ion, and neutral temperatures. Profiles can be generated with altitude, latitude, longitude, year, month, day-of-year, or time of day (UT or LT) as the independent variable.
As a new output parameter users can now also list and plot the column-integrated Total Electron Content (TEC) from the start of the ionosphere at 60 km vertically up to a user-specified upper boundary. TEC is the most important ionospheric parameter for many space applications since the time delay of electromagnetic signals is directly proportional to TEC. In addition the percentage of electron content above the F peak is given so that users can get an estimate of the relative importance of the bottomside and topside ionosphere for the TEC.
For several of its parameters, IRI gives users a choice between a standard representation and a model for specific applications. So far IRIWeb only provides the standard model. The new interface now also includes the different model options. These options include (1) the choice between the standard URSI model and the older International Radio Consultative Committee (CCIR) model for the F2 peak density - the International Union of Radio Science (URSI) generally provides better results over the oceans, and the CCIR model has slight advantages over the Northern Hemisphere continents; (2) the choice between two models for the bottomside thickness parameter B0 - of the two the Table-option is based on a larger set of data and recommended as the standard, whereas the Gulyaeva-option has proven to be more reliable at low latitudes; (3) the choice between the old and new models for the ion composition in the middle and lower ionosphere - the newer DANILOV-95 option is the recommended standard. The earlier model, IRI-86, has been kept as an option for test and evaluation purposes.
In addition this newest version of IRI includes several technical corrections that were noted by users. Also updated was the IRI indices file with the most recent observations and predictions of the 12-month smoothed values of the sunspot number (Rz12) and the Ionospheric Global (IG) index.
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